Electronic switches, such as MOSFETs (metal oxide semiconductor field effect transistors) or IGBTs (insulated gate bipolar transistors), are widely used as switches in a variety of different electric or electronic applications.
Automotive on-board power supply systems in modern cars include at least two power supply sub-systems each having a battery. A first sub-system includes the starter, while a second sub-system includes other electric loads, such as lamps, a radio, a car navigation system, window lifters, seat adjustments, etc. The first sub-system may further include a generator for charging or re-charging the batteries in both sub-systems. The two sub-system are connected via an electronic switch so as to balance the voltage in the two sub-systems and so as to allow the generator to charge the batteries in both sub-systems.
When the starter is actuated in such a power supply system it draws a huge current which may cause the supply voltage of the battery in the first sub-system to drop. In order to prevent a voltage drop of the supply voltage in the second sub-system, the electronic switch can be opened in those time periods in which the starter is actuated. When the switch is open, the battery in the second circuit supplies the loads of the second sub-system, so that actuating the starter does not cause these loads to be deactivated or switched off.
The electronic switch used to connected or disconnect the two subsystem may be implemented as a high-side switch that is driven using a charge pump, where the switch is switched on when the charge pump is activated by a control signal and is switched off when the charge pump is deactivated by the control signal. However, high-side switches that are driven using a charge pump have a relatively long switching delay. The “switching delay” is the time delay between the time of applying the control signal to the charge pump and the time of switching off the electronic switch. This delay may be in the range of several 10 ms (microseconds).
The electronic switch may be switched off each time an operating state is detected that indicates that the voltage in the second system is about to drop. However, due to the delay time, the voltage may significantly drop between the time at which this operating state is detected and the time at which the electronic switch interrupts the connection between the two sub-systems.
There is, therefore, a need to provide an electronic circuit with a switch, in particular with a high-side switch, in which the switch can be switched off with a low delay time.